Browsing Chemistry by Author "Reynolds, P.A."
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Goodwin, J.W.; Hughes, R.W.; Kwaambwa, H.M.; Reynolds, P.A. (Elseview Science B.V. www.elsevier.nl/locate/colsurfa, NaN, 2000)[more][less]
Abstract: A series of well characterised cis-polyisoprene polymers have been added to dispersions of PHS coated PMMA particles in dodecane. At a molecular weight of 8000 g mol−1 and above, these systems showed phase separation at low particle volume fractions and above a critical polymer concentration. The rate of separation has been shown to be influenced by the viscosity of the polymer. At high polymer and particle volume fractions long lived metastable phases occurred. Above a critical concentration these were viscoelastic indicating an appreciable change in diffusion dynamics with two relaxation processes present. A significant Bingham yield stress was also observed. The Asakura Oosawa potential was not able to describe the observed rheological properties. At a molecular weight of 1000 g mol−1 no phase separation was observed. At high particle concentrations the yield stress was found to reduce with the addition of polymer. This was due to the polymer acting as a ‘solvent’ and penetrating the stabilising layer on the particles. URI: http://hdl.handle.net/10311/329 Files in this item: 1
Phase separation behaviour.pdf (2.723Mb) -
Goodwin, J.W.; Hughes, R.W.; Reynolds, P.A.; Kwaambwa, H.M. (Elsevier B.V. www.elsevier.com/locate/colsurfa, NaN, 2004)[more][less]
Abstract: A series of well characterised cis-poly(isoprene) (PIP) polymers (Mw = 1180, 8000, 28 300, 31 500, 86 000, 115 000 and 130 000) have been added to dispersions of poly(12-hydroxystearic acid) (PHS) coated poly(methylmethacrylate) (PMMA) particles in dodecane. The ratio of particle size to adsorbed layer was also varied. For a given added polymer molecular weight, the polymer concentration in the continuous phase covered the dilute, semi-dilute and concentrated regimes as defined by the critical concentrations c and c . The viscosity behaviour of latex dispersions with added polymer were similar for all latex/polymer combinations except when polymer Mw = 1180 was added. In the latter case, the effect of adding polymer reduced both the viscosity and shear thinning behaviour. This supports the contention that the lower molecular weight polymer acts more like a diluent than a depletent. The behaviour of the viscosity ratio (the viscosity of the dispersion relative to that of the medium) as a function of polymer concentration increased with an increase in the polymer concentration until some critical concentration (cmax) for all polymers except for a polymer molecular weight 1180 Daltons. The addition of the polymer Mw = 8000 gave the highest viscosity ratio values in the polymer concentration range studied. It was found that the viscosity of all latex/polymer combinations decreased with an increase in temperature. The results suggest that the viscosity behaviour cannot be explained on the basis of a simple steric–elastic model and require a modified theoretical treatment. URI: http://hdl.handle.net/10311/324 Files in this item: 1
Viscosity behaviiour of particles.pdf (4.522Mb) -
Kwaambwa, H.M.; Goodwin, J.W.; Hughes, R.W.; Reynolds, P.A. (Elsevier B.V. www.elsevier.com/locate/colsurfa, NaN, 2007)[more][less]
Abstract: Aseries of six well characterised homopolymers of cis-polyisoprene (PIP) ranging from 1180 to 115,000 molecular weight were utilised to explore viscosity and the scaling relationship between viscosity and concentration in dodecane (good solvent). For each polymer molecular weight, the relative viscosity of PIP in dodecane at 298K was measured at several polymer concentrations using capillary viscometry. The linear extrapolation of experimental data based on Huggins, Kramer, Martin and Schulz-Blaschke equations was used to find the intrinsic viscosity at infinite dilution for each polymer molecular weight. The single-point method of evaluation of the intrinsic viscosity was also used for comparison. The Mark-Houwink fit of the data gave power index of 0.72 indicating that dodecane is good solvent for PIP and the latter exists in solution as open flexible coil. Both the radius of gyration and critical chain overlap concentration, c*, were derived from measured intrinsic viscosities. Plot of the relative viscosities versus the scaled concentration c/c*, resulted in single curve with slope value 4.44×10−2 and correlation coefficient r2 = 0.996, indicating good linear fit. URI: http://hdl.handle.net/10311/328 Files in this item: 1
Viscosity molecular weight.pdf (3.079Mb)
Now showing items 1-3 of 3